In a radio communication system, in a noise dominant network or a dead-spot, in general, a relay node may need to be involved, which aims at resolving the coverage problem. The relay system has already been adopted, as described in Non-Patent Document 1 below, in IEEE (The Institute of Electrical and Electronic Engineers) 802.16j standard. In addition, the relay system will be potentially developed also in new cellular phone standards such as long-term evolution advanced (LTE-advanced) for which standardization works have been in progress by the standardization body 3GGP (3rd Generation Partnership Project). Details of these are described, for example, in Non-Patent Documents 2-8 below.